This invention relates to methods for removing inorganic material, particularly rhodium- and iridium-containing films, on substrates such as semiconductor-based substrates.
Films of metals and metal oxides, particularly rhodium (Rh) and iridium (Ir), are becoming important for a variety of electronic and electrochemical applications. These metal-containing films are generally unreactive toward silicon and metal oxides, resistant to diffusion of oxygen and silicon, and are good conductors. Oxides of these metals also possess these properties, although perhaps to a different extent. Thus, films of Rh and Ir have suitable properties for a variety of uses in semiconductor-based substrates (e.g., integrated circuits). For example, they can be used in integrated circuits for electrical contacts. They are particularly suitable for use as barrier layers between the dielectric material and the silicon substrate in memory devices, such as ferroelectric memories. Furthermore, they may even be suitable as the plate (i.e., electrode) itself in capacitors. Iridium oxide is of particular interest as a barrier layer because it is very conductive (30-60 xcexcxcexa9-cm) and is inherently a good oxidation barrier.
In the fabrication of semiconductor integrated circuits (ICs), various layers of inorganic material are patterned in desired shapes. The resulting inorganic layers form individual devices and interconnect structures within the IC. Patterning conventionally includes masking an underlying layer with an organic resist material, such as photoresist, exposing the resist, and removing exposed areas of the mask to form a patterned mask layer. The exposed inorganic layer underlying the patterned mask layer is then removed using an appropriate etchant. The patterned mask layer is then removed;
Etching is a process for removing unwanted material (i.e., partial or complete layers of material) from a surface (e.g., the surface of a semiconductor-based substrate). Organic or inorganic material, which may be patterned or unpatterned, of a substrate surface can be removed using an etching technique. Ideally, etching should precisely remove material that is not covered by a patterned mask layer (i.e., material that is xe2x80x9cexposedxe2x80x9d when a patterned mask layer is used).
The etchant is typically chemically varied according to the type of material being etched. Etchants are characterized as isotropic or anisotropic. Isotropic etchants remove material in all directions at the same rate. Anisotropic etchants do not remove material in all directions at the same rate. Etchants are further characterized as being selective or non-selective, depending on their ability to differentiate between material that they effectively etch. Selective etchants remove different types of material at different rates.
Etching can occur in a wet or dry processing environment. Wet etching refers to the contact of a substrate surface with a liquid chemical etchant. Material is removed as an agitated liquid or spray, for example, passes over the substrate surface. Dry etching typically refers to the contact of a substrate surface with a gaseous etchant, typically a plasma etchant, although chemical etching is also used. While wet etchants have many preferable characteristics as compared to dry etchants, dry etchants are most often used for anisotropic etching and can be used in semiconductor fabrication without the need to dry the substrate being processed after an etching step. The added step of drying the substrate that is required when using a conventional wet etchant adds to the cost of semiconductor device fabrication. Another advantage of etching with a dry etchant is that it often decreases the safety hazards associated with wet etchants due to the relatively small amount of chemicals utilized in the dry etchant.
One of the challenges for integrating Rh and Ir into semiconductor-based substrates is the ability to dry etch such a metal. These metals are generally unreactive and are known to form nonvolatile products with many common etch gases. One report of chemically etching an iridium film appears in Xu et al., Proc. Mater. Res. Soc., Fall 1998, which uses XeF2. One observation indicated in this report is that no etching is observed without the presence of bare silicon. Additionally, XeF2 is an expensive material and would add an undesirable cost to the semiconductor manufacturing process.
Thus, an etching composition and method of etching (or otherwise removing) rhodium- and iridium-containing films from substrates, such as in the fabrication of semiconductor-based substrates, particularly ICs, is needed. Preferably, a method is needed that achieves an effective, highly uniform removal of material across a substrate.
A method for removing (preferably, etching) a metal-containing material is provided. The method includes providing a substrate having an exposed metal-containing material that includes rhodium, iridium, or a combination thereof, and exposing the substrate to a composition (preferably, an etching composition) that includes at least one halogen-containing gas (i.e., halide gas) to remove at least a portion of the metal-containing material from the substrate. The substrate is preferably a semiconductor-based substrate or substrate assembly, such as a wafer, used in semiconductor structures, although the metal-containing material can be on a wide variety of substrates, including the interior of an etching chamber or deposition chamber. Typically and preferably, the metal-containing films are electrically conductive. The resultant films can be used as barrier layers or electrodes in an integrated circuit structure, particularly in a memory device such as a ferroelectric memory device. For example, the metal-containing material can form an electrode in a high-k dielectric capacitor (i.e., a capacitor that includes a material having a high dielectric constant).
The metal-containing film can include pure iridium, pure rhodium, or an alloy containing iridium and/or rhodium and one or more other metals (including transition metals, main group metals, lanthanides) and/or metalloids from other groups in the Periodic Chart, such as Si, Ge, Sn, Pb, Bi, etc. Furthermore, for certain preferred embodiments, the metal-containing film can be an oxide, nitride, sulfide, selenide, silicide, or combinations thereof. Thus, in the context of the present invention, the term xe2x80x9cmetal-containing filmxe2x80x9d includes, for example, relatively pure films of iridium, relatively pure films of rhodium, alloys of iridium or rhodium with each other or with other Group VIII transition metals such as nickel, palladium, platinum, iron, ruthenium, and osmium, metals other than those in Group VIII, metalloids (e.g., Si), or mixtures thereof. The term also includes complexes of iridium, rhodium, iridium alloys, or rhodium alloys with other elements (e.g., O, N, and S). The terms xe2x80x9csingle transition metal filmxe2x80x9d or xe2x80x9csingle metal filmxe2x80x9d refer to relatively pure films of iridium or rhodium. The terms xe2x80x9ctransition metal alloy filmxe2x80x9d or xe2x80x9cmetal alloy filmxe2x80x9d refer to films of iridium or rhodium in alloys with each other or other metals or metalloids, for example. Thus, herein the metal-containing material is also referred to as an iridium- and/or rhodium-containing material.
The substrate can have a patterned mask layer thereon, wherein the iridium- and/or rhodium-containing material removed from the substrate includes exposed iridium- and/or rhodium-containing material under the patterned mask layer. The iridium- and/or rhodium-containing material can also be removed from the substrate in an unpatterned manner (i.e., without the presence of a patterned mask layer on the substrate).
In one embodiment, the method of removing an iridium- and/or rhodium-containing material uses a preferred composition that includes at least one halogen-containing (i.e., halide) gas and at least one auxiliary gas. The halide gas may be capable of removing material (e.g., etching) without an additional component, depending on the material being removed. If; however, the halide gases are not capable of removing material in and of themselves, an auxiliary gas is used that is capable of enhancing the removal. Whether an auxiliary gas is used or not, the composition may also optionally include a source of oxygen because the resultant rhodium and iridium oxyhalides are generally volatile.
The halide gas is a halogen-containing gas (i.e., a gas containing one or more elements from Group VIIA (Group 17) of the Periodic Table). For certain embodiments, this does not include XeF2. For other embodiments, the halogen-containing gas is one that optionally includes hydrogen or elements from Groups IIIA (Group 13), IVA (Group 14), VA (Group 15), VIA (Group 16) of the Periodic Table, or mixtures thereof. Preferably, the auxiliary etching component is selected from the group of carbon monoxide (CO), nitric oxide (NO), alkylphosphines, isocyanides, and combinations thereof. Preferably, the source of oxygen is selected from the group of oxygen (O2), NO, N2O, NO2, oxyhalides, H2O, H2O2, CO2, SO2, SO3, O3, and combinations thereof.